159 research outputs found
Observation of spin-orbit magnetoresistance in metallic thin films on magnetic insulators
A magnetoresistance effect induced by the Rashba spin-orbit interaction was
predicted, but not yet observed, in bilayers consisting of normal metal and
ferromagnetic insulator. Here, we present an experimental observation of this
new type of spin-orbit magnetoresistance (SOMR) effect in a bilayer structure
Cu[Pt]/Y3Fe5O12 (YIG), where the Cu/YIG interface is decorated with nanosize Pt
islands. This new MR is apparently not caused by the bulk spin-orbit
interaction because of the negligible spin-orbit interaction in Cu and the
discontinuity of the Pt islands. This SOMR disappears when the Pt islands are
absent or located away from the Cu/YIG interface, therefore we can
unambiguously ascribe it to the Rashba spin-orbit interaction at the interface
enhanced by the Pt decoration. The numerical Boltzmann simulations are
consistent with the experimental SOMR results in the angular dependence of
magnetic field and the Cu thickness dependence. Our finding demonstrates the
realization of the spin manipulation by interface engineering.Comment: 12 pages, 4 figures, 14 pages in supplementary. To appear on Science
Advance
A Novel Color Parameter As A Luminosity Calibrator for Type Ia Supernovae
Type Ia supernovae (SNe Ia) provide us with a unique tool for measuring
extragalactic distances and determining cosmological parameters. As a result,
the precise and effective calibration for peak luminosities of SNe Ia becomes
extremely crucial and thus is critically scrutinized for cosmological
explorations. In this Letter, we reveal clear evidence for a tight linear
correlation between peak luminosities of SNe Ia and their colors days after the maximum denoted by . By introducing such
a novel color parameter, , this empirical correlation allows us
to uniformly standardize SNe Ia with decline rates in the range
of and to reduce scatters in estimating their peak
luminosities from mag to the levels of 0.18 and 0.12 mag in the
and bands, respectively. For a sample of SNe Ia with insignificant
reddenings of host galaxies [e.g., E(B-V)_{host}\lsim 0.06 mag], the scatter
drops further to only 0.07 mag (or 3-4% in distance), which is comparable to
observational accuracies and is better than other calibrations for SNe Ia. This
would impact observational and theoretical studies of SNe Ia and cosmological
scales and parameters.Comment: 13 pages, including 3 figures. To appear in ApJL (2005 Feb issue
Hot isostatic pressing of in-situ TiB/Ti-6Al-4V composites with novel reinforcement architecture, enhanced hardness and elevated tribological properties
In this study, titanium borides reinforced Ti-6Al-4V composites have been successfully prepared by hot isostatic pressing (HIPing). The microstructure of the as-fabricated samples was investigated using X-ray diffraction technique, secondary electron microscopy and electron backscatter diffraction and the mechanical properties evaluated through micro-hardness and wear resistance measurements together with nano-indentation. It was found that during HIPing the additive particles TiB2 have transformed into TiB needles which tend to decorate at prior particle boundaries of the consolidated powder particles to form a network structure. Under the same HIPing condition, the needles became increasingly coarser and agglomerated with increased addition of TiB2. The micro-hardness of the synthesized materials increased with increased volume fraction of TiB. Nano-indentation measurement demonstrates that the TiB network structure shows much higher nanohardness than the surrounding matrix regions. The friction coefficient of the synthesized composites decreased continuously with increased volume fraction of TiB, indicating improved wear resistance. High resolution transmission electron microscopy analysis on wear debris revealed the formation of a series of oxides suggesting that chemical reaction between alloy elements and oxygen in air may have happened. It is thus believed that the wearing of the current samples is a result of both friction and chemical reaction
Eclipsing Binaries From the CSTAR Project at Dome A, Antarctica
The Chinese Small Telescope ARray (CSTAR) has observed an area around the
Celestial South Pole at Dome A since 2008. About light curves in the i
band were obtained lasting from March to July, 2008. The photometric precision
achieves about 4 mmag at i = 7.5 and 20 mmag at i = 12 within a 30 s exposure
time. These light curves are analyzed using Lomb--Scargle, Phase Dispersion
Minimization, and Box Least Squares methods to search for periodic signals.
False positives may appear as a variable signature caused by contaminating
stars and the observation mode of CSTAR. Therefore the period and position of
each variable candidate are checked to eliminate false positives. Eclipsing
binaries are removed by visual inspection, frequency spectrum analysis and
locally linear embedding technique. We identify 53 eclipsing binaries in the
field of view of CSTAR, containing 24 detached binaries, 8 semi-detached
binaries, 18 contact binaries, and 3 ellipsoidal variables. To derive the
parameters of these binaries, we use the Eclipsing Binaries via Artificial
Intelligence (EBAI) method. The primary and the secondary eclipse timing
variations (ETVs) for semi-detached and contact systems are analyzed.
Correlated primary and secondary ETVs confirmed by false alarm tests may
indicate an unseen perturbing companion. Through ETV analysis, we identify two
triple systems (CSTAR J084612.64-883342.9 and CSTAR J220502.55-895206.7). The
orbital parameters of the third body in CSTAR J220502.55-895206.7 are derived
using a simple dynamical model.Comment: 41 pages, 12 figures; published online in ApJ
Photometry of Variable Stars from Dome A, Antarctica
Dome A on the Antarctic plateau is likely one of the best observing sites on
Earth thanks to the excellent atmospheric conditions present at the site during
the long polar winter night. We present high-cadence time-series aperture
photometry of 10,000 stars with i<14.5 mag located in a 23 square-degree region
centered on the south celestial pole. The photometry was obtained with one of
the CSTAR telescopes during 128 days of the 2008 Antarctic winter.
We used this photometric data set to derive site statistics for Dome A and to
search for variable stars. Thanks to the nearly-uninterrupted synoptic
coverage, we find 6 times as many variables as previous surveys with similar
magnitude limits. We detected 157 variable stars, of which 55% are
unclassified, 27% are likely binaries and 17% are likely pulsating stars. The
latter category includes delta Scuti, gamma Doradus and RR Lyrae variables. One
variable may be a transiting exoplanet.Comment: Accepted for publication in the Astronomical Journal. PDF version
with high-resolution figures available at
http://faculty.physics.tamu.edu/lmacri/papers/wang11.pd
Gattini 2010: Cutting Edge Science at the Bottom of the World
The high altitude Antarctic sites of Dome A and the South Pole offer intriguing locations for future large scale optical astronomical
Observatories. The Gattini project was created to measure the optical
sky brightness, large area cloud cover and aurora of the winter-time
sky above such high altitude Antarctic sites. The Gattini-DomeA camera
was installed on the PLATO instrument module as part of the Chinese-led
traverse to the highest point on the Antarctic plateau in January 2008.
This single automated wide field camera contains a suite of Bessel
photometric filters (B, V, R) and a long-pass red filter for the
detection and monitoring of OH emission. We have in hand one complete
winter-time dataset (2009) from the camera that was recently returned
in April 2010.
The Gattini-South Pole UV camera is a wide-field optical camera that in
2011 will measure for the first time the UV properties of the
winter-time sky above the South Pole dark sector. This unique dataset
will consist of frequent images taken in both broadband U and B filters
in addition to high resolution (R similar to 5000) long slit
spectroscopy over a narrow bandwidth of the central field. The camera
is a proof of concept for the 2m-class Antarctic Cosmic Web Imager
telescope, a dedicated experiment to directly detect and map the
redshifted lyman alpha fluorescence or Cosmic Web emission we believe
possible due to the unique geographical qualities of the site.
We present the current status of both projects
Photometric Variability in the CSTAR Field: Results From the 2008 Data Set
The Chinese Small Telescope ARray (CSTAR) is the first telescope facility
built at Dome A, Antarctica. During the 2008 observing season, the installation
provided long-baseline and high-cadence photometric observations in the i-band
for 18,145 targets within 20 deg2 CSTAR field around the South Celestial Pole
for the purpose of monitoring the astronomical observing quality of Dome A and
detecting various types of photometric variability. Using sensitive and robust
detection methods, we discover 274 potential variables from this data set, 83
of which are new discoveries. We characterize most of them, providing the
periods, amplitudes and classes of variability. The catalog of all these
variables is presented along with the discussion of their statistical
properties.Comment: 38 pages, 11 figures, 4 tables; Accepted for publication in ApJ
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